There have been proposed several kinds of tires designed to be safe even in the case of a puncture or other loss of air pressure. They include, for example, a safety tire having a support of elastic material in the tire, a dual structured tire having an independent toroidal air-tight compartment in the tire, and a reinforced tire with the side wall or shoulder reinforced with an elastic reinforcing layer attached to the inside thereof.
The first two types have a problem with increased weight (undesirable for a high-speed tire) and increased production cost. The last type is not strong enough to firmly support the load.
Accordingly, it is an object of the present invention to provide a new radial tire which, despite its structure is entirely different from that of the above-mentioned conventional tires, provides as good a ride comfort and stable maneuverability as the ordinary tires during normal driving conditions and yet continues to run safely even when the tire pressure abruptly decreases due to puncture during high speed driving on a highway.
For safe driving, the tire should be firmly held in position on the rim. Heretofore, this has been achieved mainly by the frictional force which is generated between the bead and the bead seat as the bead is pressed against the bead seat by the tire pressure. Therefore, the power to hold the tire on the rim decreases as the tire pressure decreases. In an extreme case where the tire pressure has decreased rapidly due to puncture and the steering wheel is quickly turned, the tire bead separates from the bead seat and falls into the well on account of the lateral force applied to the tire. As a result, the tire is completely displaced, which leads to a serious accident.
The separation of the tire bead takes place in the following sequence. The cornering of the car produces a lateral force which moves the tread in the axial direction of the rim. The movement of the tread produces a moment of rotation around the bead. When the tire pressure is low, the moment of rotation lifts the heal of the bead, and decreases the frictional force between the bead and the bead seat to such an extent that the bead slips out of place in the inward direction of the tire axis. In this state, the bead core loses tension for keeping the tire on the rim and thus falls into the well.
It is another object of the present invention to provide a radial tire-rim assembly which can run safely even when the tire pressure has decreased. The feature of the radial tire-rim assembly is due to the unique structure of the tire and rim. That is, the bead has a toe extending inward in the radial direction of the tire and the rim has an annular groove to mate with said toe. The toe-groove combination prevents the bead from falling into the well when the bead receives a lateral force.